Hans makes a compelling case (extended article) that the Supreme Court sets a dangerous precedent when it relies on "international opinion" in deciding a case. The risk according to Hans, is that these "international norms" are usually hostile to our basic civil liberties and are "vague and manipulable" and therefore, can be applied selectively to push a particular ideology/agenda.

Hans expands on this point,

Courts should not rely on "international opinion" to decide cases, since it is vague and manipulable. So-called international law is applied selectively by lawyers and judges, who cite real or imagined "international law" to push the ideological goals they support, while ignoring actual international court rulings they don't like, like foreign court rulings barring punitive damages or limiting damages under the Warsaw Convention (as in Olympic Airways v. Husain).

Left-wing lawyers take vague international treaties and interpret them as mandating liberals' ideological wishlists, like restricting criticism of Islam and minority religions as "hate speech," banning Mother's Day as sexist, and mandating quota-based affirmative action. For example, the CEDAW equal-rights treaty has been construed by an international committee as requiring "redistribution of wealth," "affirmative action," "gender studies" classes, government-sponsored "access to rapid and easy abortion," and "the application of quotas and numerical goals." Never mind that most countries don't even have affirmative action.